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Core Java - Interview Questions and Answers for 'Static' - 64 question(s) found - Order By Newest

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 Q1. What do you mean by "Java is a statically typed language" ?Core Java
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Ans. It means that the type of variables are checked at compile time in Java.The main advantage here is that all kinds of checking can be done by the compiler and hence will reduce bugs.

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 Q2. How can we run a java program without making any object?Core Java
Anonymous
Ans. By putting code within static method. With Java 6 and earlier versions, even static block can be used.

  Sample Code for static block

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 Q3. Difference between Static and Singleton Class ?Core Java2016-11-30 21:00:43

Ans. 1. Static class is a class which cannot be instantiated and all its members are static whereas Singleton is the class that only permit creation of single object and then the object is reused.

2. As there is no object in Static class, it cannot participate in runtime Polymorphism.

3. As Static class doesnt allow creating objects and hence it cannot be serialized.

4. Static class body is initialized eagerly at application load time whereas Singleton object can be initiated eagerly using static blocks or lazily on first need.

5. Its not recommended to use pure static class as it fails to use many OOPs concepts.

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 Q4. What are the advantages and disadvantages of static variables and static methods ?Core Java
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Ans. Advantages

Can do meta object operations ( like validating something before creating objects , keep count of number of objects )

Can do operations which have nothing to do with objects but still you want them to be tied to Class.

Disadvantages

Commonly used to static variables sometime leads to problems due to access by different objects.

Are not tied to objects so doesn't reflect pure Object Oriented approach.

Needs to be synchronized so as to avoid update conflicts by mutiple objects and threads.

Some limitation in testing as not all frameworks have facility to mock them. Powermock has but Mockito doesnt

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 Q5. Can we declare static variables as transient ?Core Java2017-01-12 11:12:48

Ans. It's weird that compiler doesn't complain if we declare transient with static variable because it makes no sense. At least a warning message saying "transient is useless in this situation" would have helped with code cleaning.

Static variables are never serialized and transient is an indication that the specified variable shouldn't be serialized so its kind of double enforcement not to serialize.

It could be that as it makes no different to the variable behavior and hence using both keywords with a variable are permitted.

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 Q6. Which of the following can be marked static ?

a. Methods , Variables and Initialization Blocks.
b. Methods , Variables , Initialization Blocks and Outer Classes and nested Classes.
c. Methods , Variables , Initialization Blocks and Outer Classes.
d. Methods , Variables , Initialization Blocks and nested Classes
Core Java
Anonymous
Ans. Methods , Variables , Initialization Blocks and nested Classes

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 Q7. What is the difference between the following two code lines ?

1. new OuterClass().new InnerClass();

2. new OuterClass.InnerClass();
Core Java2016-06-30 14:45:37

Ans. In first case we are trying to initialize Inner class object using the instance of Outer Class whereas in second case we are trying to initialize the Inner class object directly using the Outer class name.

In second case , Inner class is "static inner class" as we cannot access "non static inner class" using Classname alone.

In first case, the inner class could be either "static inner class" or "non static inner class".

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 Q8. What are concepts introduced with Java 5 ?Core Java
Anonymous
Ans. Generics , Enums , Autoboxing , Annotations and Static Import.

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 Q9. Can we serialize static variables ?Core Java
Anonymous
Ans. No. Only Object and its members are serialized. Static variables are shared variables and doesn't correspond to a specific object.

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 Q10. Can we access instance variables within static methods ?Core Java
Anonymous
Ans. Yes.we cannot access them directly but we can access them using object reference.Static methods belong to a class and not objects whereas non static members are tied to an instance. Accessing instance variables without the instance handler would mean an ambiguity regarding which instance the method is referring to and hence its prohibited.

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 Q11. Similarity and Difference between static block and static method ?Core Java
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Ans. Both belong to the class as a whole and not to the individual objects. Static methods are explicitly called for execution whereas Static block gets executed when the Class gets loaded by the JVM.

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 Q12. In which cases , moving methods to utility class could be useful ?Core Java

Ans. It could be worthy to move a method to util class if the method needs to be shared, doesn't require polymorphic behavior and need not be overridden in special cases.

Don't belong to one group through is-a relationship ( You can share through parent class method )

Don't implement a specific interface ( java 8 default methods )

Doesn't involve complex computing as you will be loosing the benefit of object state with just static method.

Doesn't require polymorphic behavior as static methods don't participate in runtime polymorphism.

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 Q13. When are static variables loaded in memory ?Core Java
Anonymous
Ans. They are loaded at runtime when the respective Class is loaded.

  Sample Code for static variable

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 Q14. Can we override static methods ? Why ?Core Java
Anonymous
Ans. No.

Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

A static method is not associated with any instance of a class so the concept of overriding for runtime polymorphism using static methods is not applicable.

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 Q15. What is a Static import ?Core Java
Anonymous
Ans. By static import , we can access the static members of a class directly without prefixing it with the class name.

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 Q16. How can we create objects if we make the constructor private ?Core Java
Anonymous
Ans. We can do so through a static public member method or static block.

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 Q17. Difference between nested and inner classes ?
Anonymous
Ans. Inner class is a type of nested class.

Inner classes are non static nested classes i.e the one that are associated with the instance of outer class.

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 Q18. Difference between static vs. dynamic class loading?Core Java
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Ans. static loading - Classes are statically loaded with Java new operator.

dynamic class loading - Dynamic loading is a technique for programmatically invoking the functions of a class loader at run time.

Class.forName (Test className);

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 Q19. Is it possible to compile and run a Java program without writing main( ) method?
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Ans. Yes, it is possible by using a static block in the Java program.

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 Q20. Will the following program display ""Buggy Bread"" ?

class Test{
   static void display(){
      System.out.println(""Buggy Bread"");
   }
}

class Demo{
   public static void main(String... args){
      Test t = null;
      t.display();
   }
}
Core Java
Admin
info@buggybread.com
Ans.  Yes. static method is not accessed by the instance of class. Either you call it by the class name or the reference.

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 Q21. Can we use static method definitions in Interfaces ?Core Java
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Ans. Yes, Effective Java 8.

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 Q22. Why can't we use this in static context ?Core Java
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Ans. Static methods can be called using instance references wherein this would have made sense but static method can also be called using Class name wherein this would mean nothing and hence forbidden.

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 Q23. Which of the following cannot be marked static ?

a. Constructors , Classes ( Outer ) , Classes ( nested ), Interfaces , Local variables , Inner Class methods and instance variables.
b. Constructors , Classes ( Outer ) , Interfaces , Local variables , Class variables , Class Methods , Inner Class methods and instance variables.
c. Constructors , Classes ( Outer ) , Interfaces , Local variables , Inner Class methods and instance variables.
d. Constructors , Classes ( Outer ) , Classes (Nested), Interfaces , Local variables , Inner Class methods and instance variables
Anonymous
Ans. Constructors , Classes ( Outer ) , Interfaces , Local variables , Inner Class methods and instance variables.

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 Q24. What is the use of static keyword in Java ?Core Java2017-01-09 13:32:24

Ans. static keyword is used to specify that the respective programming construct ( method , variable ) belongs to the class and not to its instance and is supposed to be shared by all instances of the class.

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 Q25. How can we ensure thread safety in static method ?Core Java2017-08-27 07:49:53

Ans. By using synchronized static method or synchronized block

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 Q26. Can static method access instance variables ?Core Java
Anonymous
Ans. Though Static methods cannot access the instance variables directly, They can access them using instance handler.

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 Q27. Does java allow overriding static methods ?Core Java
Anonymous
Ans. No. Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

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  Q28. Explain static blocks in Java ?Core Java
Anonymous
Ans. A static initialization block is a normal block of code enclosed in braces, { }, and preceded by the static keyword. Here is an example:

static {
// whatever code is needed for initialization goes here
}

A class can have any number of static initialization blocks, and they can appear anywhere in the class body. The runtime system guarantees that static initialization blocks are called in the order that they appear in the source code.

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 Q29. Explain Static nested Classes ?
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Ans. The accessibility (public, protected, etc.) of the static nested class is defined by the outer class.

A static nested class is not an inner class, it's a top-level nested class.

The name of the static nested class is expressed with OuterClassName.NestedClassName syntax.

When you define an inner nested class (or interface) inside an interface, the nested class is declared implicitly public and static.

Static nested classes can be declared abstract or final.

Static nested classes can extend another class or it can be used as a base class.

Static nested classes can have static members.

Static nested classes can access the members of the outer class (only static members, obviously).

The outer class can also access the members (even private members) of the nested class through an object of nested class. If you don't declare an instance of the nested class, the outer class cannot access nested class elements directly.

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 Q30. Can we use "this" within static method ? Why ?Core Java
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Ans. No. Even though "this" would mean a reference to current object id the method gets called using object reference but "this" would mean an ambiguity if the same static method gets called using Class name.

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 Q31. What will happen if static modifier is removed from the signature of the main method?
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Ans. Program throws "NoSuchMethodError" error at runtime .

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 Q32. Will the static block be executed in the following code ? Why ?

class Test
{
static
{
System.out.println("Why I am not executing ");
}
public static final int param=20;
}

public class Demo
{
public static void main(String[] args)
{
System.out.println(Test.param);
}
}
Admin
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Ans. No the static block won't get executed as the referenced variable in the Test class is final. Compiler replaces the content of the final variable within Demo.main method and hence actually no reference to Test class is made.

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 Q33. Will static block for Test Class execute in the following code ?

class Test
{
static
{
System.out.println("Executing Static Block.");
}
public final int param=20;

public int getParam(){
return param;
}
}

public class Demo
{
public static void main(String[] args)
{
System.out.println(new Test().param);
}
}
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Ans. Yes.

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 Q34. Which of the following syntax is correct ?

import static java.lang.System.*;

or

static import java.lang.System.*;
Core Java
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Ans. import static java.lang.System.*;

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 Q35. Can we access Interface static method using Interface references ?
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Ans. No, only using Interface Name.

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 Q36. Can we have default method with same name and signature in the derived Interface as the static method in base Interface and vice versa ?
Admin
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Ans. Yes , we can do that as static methods are not accessible using references and hence cannot lead to conflict. We cannot do inverse as Default methods cannot be overridden with the static methods in derived interface.

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 Q37. Shouldn't we make a class with all static members is its just expected to be executed as a standalone program with just one thread. Moreover Lets assume that there is no runtime Polymorphism required and there is no need for serialization ?Design
Admin
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Ans. Still No in case we are making use of inheritance. we may have problem wherein we have program flow moving across common inherited method and specific methods of the derived class. call made to another static method in the parent class will only access the static class of the Parent class irrespective of the call from any of the derived class.

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 Q38. Why is a constant defined as a static final in Java?Core Java
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Ans. Final makes sure that the value doesn't change after initialization and static makes sure that there is only one copy that can be shared across objects.

Making it non static will unnecessarily create a different copy per object wherein the same value will kept for all copies ( as its final and cannot be changed ).

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 Q39. Can we initialize member variables within static block ?
Admin
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Ans. Static block is like static method that gets executed upon class loading. The way static method allows accessing member variables ( using object references only ), the same static block can also access and initialize member variables.

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 Q40. When are static and instance methods resolved ? During compile time or Runtime ?
Admin
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Ans. Static methods are resolved during compile time and hence they cannot participate in runtime polymorphism. Instance methods are resolved during runtime.

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